This invention relates to a flexible pipe gasket and, in particular, to a flexible gasket that is ideally suited to form a fluid tight seal between a pipe section and a wall opening into which the pipe section is fitted.
In U.S. Pat. No. 3,787,061 an elastomeric pipe gasket is disclosed for sealing a pipe section within a receiving hole contained in a manhole riser. A circular retaining groove that compliments the outer periphery of the gasket is machined or otherwise formed in the pipe receiving hole of the riser wall and the gasket is seated therein. A wound spring is contained within the gasket which is designed to lock the gasket against the outside of the pipe. The ends of the spring are brought out of the gasket and are positioned within an expanded chamber formed in the riser wall. During assembly, the spring ends are engaged by a special tool that expands the spring sufficiently to permit the pipe to be inserted into the gasket. When the spring is then released it tightens the gasket against the pipe thereby completing the sealing joint. It should be noted, however, that the gasket may be pinched or rolled against the sharp edges of the retaining groove during pipe insertion and becomes torn or otherwise damaged. Expansion of the spring within the limited confines of the pipe receiving hole is oftentimes difficult to achieve. The exposed ends of the spring are susceptible to corrosion which leads to premature failure of the seal.
In U.S. Pat. No. 3,958,313, a funnel-shaped boot is disclosed that is used to join a pipe section to a manhole riser. The neck of the boot is clamped by a metal collar to the pipe section and the wide end of the boot is passed into a hole formed in the riser wall. The boot is locked within the hole by means of a special expansion band having a toggle joint which, when actuated, expands the wide end of the boot into sealing contact against the sidewall of the hole. The toggle is joined to the two ends of the band and normally holds the band in a contracted condition. To expand the band, a closing force of about 1000 pounds is exerted by a pneumatic tool directly against the toggle joint. The high pressure not only closes the joint but also destroys the toggle. Accordingly, if a fluid tight seal is not achieved on the first closure attempt, the pipe must be removed from the hole and fitted with a new sealing gasket. By the same token, if the seal must be broken for maintenance purposes or the like, the entire gasket unit must be removed and a new toggle joint expansion band inserted in the boot. Boot type seals because they protrude beyond the wall opening, the highly susceptible to being cut on the sharp front edge of the wall. Sharp rocks, tools or other types of foreign objects can also easily penetrate the exposed section of the boot during back filling or excavating operations. Lastly, it should be noted that the expandable band of the unit is continually exposed to moisture and/or other corrosive fluids carried by the system and, unless fabricated of special high priced corrosion resistant materials, will fail long before the other component parts that form the sealing joint.